This proposal tests the hypothesis that tumor necrosis factors (TNFs) and secreted forms of beta-amyloid precursor protein (sAPPs) protect neurons against amyloid beta-peptide (Abeta) toxicity by a mechanism involving the transcription factor NFkappaB and induction of antioxidant enzymes. The neurotoxicity of Abeta is mediated by reactive oxygen species (ROS) and calcium, and preliminary data showed that TNFs and sAPPs can protect hippocampal neurons against Abeta toxicity and induce NFkappaB DNA binding activity. The specific aims of this project are: 1) To test the hypothesis that TNFs and sAPPs protect cultured hippocampal neurons against Abeta toxicity by inducing activation of NFkappaB. We will characterize induction of NFkappaB DNA binding activity by TNFs and sAPPs, determine whether other agents known to activate NFkappaB are neuroprotective, and employ antisense oligonucleotides (AODNs) to IkappaB (inhibitory subunit of NFkappaB) or p50 (transcription factor subunit). 2) To test the hypothesis that activation of NFkappaB by TNFs and sAPPs prevents Abeta-induced accumulation of ROS, impairment of ion-motive ATPase activities, and elevation of [Ca2+]i. Roles of specific ROS will be examined using assays of peroxides, hydroxyl radical, superoxide and protein carbonyl. 3) To test the hypothesis that activation of the NFkappaB signaling system by TNFs and sAPPs protects neurons by inducing the expression of antioxidant enzymes and the calcium-binding protein calbindin. This will be accomplished using antioxidant enzyme activity assays, RNAse protection assays and Western blot analysis. 4) To determine whether intraventricular administration of TNFs and sAPPs to adult rat protects hippocampal synaptosomes from Abeta-induced damage. NFkappaB activity, antioxidant enzyme activities and calbindin levels following infusion of TNF and sAPPs will be quantified and correlated with effects of TNFs and sAPPs on vulnerability of synaptosomes to Abeta. 5) To test the hypothesis that the NFkappaB signaling system is activated in AD brain in a regional pattern related to selective vulnerability. NFkappaB activity will be quantified in tissue from vulnerable brain regions (middle temporal gyrus, hippocampus, inferior parietal cortex) and relatively nonvulnerable brain regions (cerebellum, occipital pole) from AD brains and age-matched "control" brains. This research will identify fundamental mechanisms of neuronal injury and neuroprotection relevant to the pathogenesis of Alzheimer's disease.